1. Field of the Invention
The present invention relates to a shaped oxide superconductor article having a cross-section of composite phase comprising an oxide phase having a superconducting transition property and a metal phase, more particularly to a shaped oxide superconductor article, such as a wire, tape and disk, containing as the metal phase an industrially inexpensive metal having a composition suitable for constituting the oxide superconductor article.
2. Description of Related Art
As a high-temperature superconducting material having a much higher superconducting transition temperature than that of prior art superconducting materials, a lanthanum-barium-copper oxide was discovered by Dr. J. G. Bednorz and Dr. K. A. Muller at the beginning of 1986, and then an yttrium-barium-copper oxide (hereinafter referred to as Y-Ba-Cu-O system) which has a transition temperature of about 90 K was discovered by Dr. Chu of Houston University in U.S.A., in the spring of 1987. Such discovery was made also in China and Japan at that time. These discoveries in succession are called the revolution of superconductors. Nowadays, fundamental studies are being made on the composition, crystal structure, properties and theory of superconducting materials, practical studies on methods of synthesizing the materials, on electronic or power electrical applications of the materials and further on research or development of new materials exhibiting superconducting transition at a higher temperature or room temperature.
In these studies, research and development, a technique of shaping the high-temperature superconducting materials holds a position as an elementary technique in power electrical applications such as a superconducting magnet. In prior art superconducting alloys or compounds, it is known that the cross-section of shaped articles is constituted by a composite phase of a superconducting phase and a metal phase. The metal phase functions as a supporter for a superconducting material while the material is being plastically worked in a long article and heat treated, as a strength-holding means during or after coiling of a superconducting wire, or as a stabilizer against the superconducting-to-normal transition in applying electric current t the article.
As a material for the metal phase of oxide superconductor articles are only known copper, copper-nickel alloys and silver, as reported by news papers, Nihon Keizai Shimbun dated Mar. 4, 1987 and Apr. 3, 1987, and Nikkei Sangyo Shimbun dated May 19, 1987. However, no details are known about these metals.
The Y-Ba-Cu-O system known as a high-temperature superconducting material is analyzed to be an oxygen-deficient type trilayered perovskite crystal. In order to shape this material in an article, for example, a long wire, it is necessary that the material is firstly powdered, charged into a metal pipe, drawn and finally reheated or resintered to revive the superconduction in the article. In the case of the metal phase being copper or copper-nickel alloy, removal of the metal phase by, for example, dissolving it with an acid is needed before reheating, as reported in, for example, Spring Meeting (100 th, Tokyo) of Japan Metal Society. This is because the copper of the metal phase is oxidized during reheating, so that the oxygen of superconducting materials is taken by the copper and the material exhibits no superconducting transition.
In the case, on the other hand, of the metal phase, being constituted by silver, there hardly occurs the above-mentioned problem, because the oxygen-dissociating pressure of silver is high at the reheating temperatures. However, since the reheating temperature is nearly as high as the melting point of silver, the silver is remarkably grown in coarser crystal grains and greatly softened, so that strength required by wires is lost. Further, there is an economical problem that silver is expensive.
Thus, in the case of using copper or copper-nickel alloys as the metal phase in shaping oxide superconductor articles, the metal phase is in fact finally lost so that any practical shaped superconductor articles cannot be made. Further, silver is also hardly technically and economically acceptable as the metal phase as mentioned above.